This invention pertains to an improved three-piece wound golf ball construction including a solid center core, an intermediate thread wound layer, and an outer cover piece. It pertains particularly to such a wound golf ball in which the core has larger diameter and decreased specific gravity so as to provide increased moment of inertia, spin rate and improved trajectory distance after being hit by any of various golf clubs.
Conventional known golf balls have either two-piece construction consisting of a center core and an outer cover with multiple dimples provided on its outer surface, or have three-piece construction consisting of a center core, an intermediate portion which may be solid or have elastomeric thread winding, and a solid dimpled cover. The cores are usually made of natural or synthetic rubber and may be either solid or have a liquid/paste form. The cover material is usually Balata or an ionomer in combination with a suitable filler material. Variations in the chemical or physical properties of the ball materials or their physical orientation can bring about changes in the golf ball characteristics, such as feel, flight distance, rebound coefficient, durability, moment of inertia, spin etc. as has been generally described in various prior art patents.
For example, U.S. Pat. No. 4,076,255 to Moore et al discloses a three-piece golf ball having a solid core formed from a cured composition comprising polybutadiene having a high cis-content, and a monomer capable of grafting, cross-linking or chain-extending the elastomer. The core having a Shore C hardness of 60-80 is wound with a conventional elastic thread and covered with a molded cover, but the core diameter is not disclosed.
U.S. Pat. No. 4,625,964 to Yamada discloses a three-piece solid golf ball having a core formed of polybutadiene with a specific gravity of at least 1.50 and a diameter not exceeding 32 mm (1.26 inch). The ball intermediate layer has a specific gravity lower than that of the core and thickness of 3.2-5.4 mm, and the cover has a thickness of 1-3 mm and a Shore D hardness not exceeding 64.
U.S. Pat. No. 4,696,475 to Tomita et al discloses a three-piece thread-wound golf ball having improved impact resiliency and increased flight distance. The core rubber and/or the winding thread contains more than 30% by weight of an isoprene-butadiene random copolymer and has core diameter of 28-30 mm (1.10-1.18 inch).
U.S. Pat. No. 4,714,253 to Nakahara et al, discloses a three-piece solid golf ball having controlled diameters, specific gravities, and hardnesses of the central core and intermediate solid layer. The central core has a diameter of 20 to 32 mm (0.79-1.26 inch), specific gravity of 1.03 to 1.25, and a Shore C hardness of 57 to 80. The solid intermediate layer has 36-40 mm. diameter, specific gravity of 1.30-2.50 and Shore C hardness of 70-83, but it does not have a thread winding.
U.S. Pat. No. 5,397,129 to Kato et al discloses a three-piece thread-wound golf ball having a solid rubber core of 23 to 34 mm (0.91-1.34 inch) diameter. Various rubber types may be used for the core, the intermediate winding thread, and the molded cover, material including butadiene and natural rubbers.
U.S. Pat. No. 5,445,387 to Maruko et al discloses a three-piece thread-wound golf ball having a solid center of high cis-polybutadiene, a conventional thread-wound intermediate rubber layer, and a cover. The core hardness is continuously increased from its center to its outer surface. The solid core diameter is 26-31 mm (1.02-1.22 inch), the intermediate layer is 39-41 mm diameter, and ball diameter is 42.5-45 mm (1.67-1.77 inch).
Also, U.S. Pat. No. 5,553,852 to Higuchi et al discloses a three-piece solid golf ball having a center core of 29-37 mm (1.14-1.46 inch) diameter, hardness of 45-80 JIS C and a specific gravity of 1.05-1.4 but greater than that of the solid intermediate layer which has thickness of 1-3.5 mm (0.039-0.138 inch) and specific gravity of 0.9-1.2. The cover has 1-3 mm (0.039-0.118 inch) thickness and is softer than the intermediate layer.
Although golf balls having various constructions and characteristics are known, important deficiencies have been found by players to exist in these known golf ball constructions and flight characteristics. Specifically, the two-piece golf balls are far inferior in the controllability that is required when a shot is made with the middle iron or short iron clubs. In addition, a two-piece golf ball provides a poor shot feeling to the player. Known three-piece Balata golf balls exhibit spin rates that are too great for good flight distance when hit with a Driver and long iron clubs. Thus, desirable improvements in golf ball construction and spin characteristics, all achieved at reduced ball manufacturing costs, have been sought.